1. Field of the Invention
The present invention relates to composite-material vibrating devices in which a plurality of material portions having different acoustic impedances are coupled, and more particularly relates to a composite-material vibrating device in which a plurality of material layers having different acoustic impedances are coupled to a vibrating member such as a piezoelectric element.
The present invention further relates to methods for fabricating a composite-material vibrating device in which a plurality of material portions having different acoustic impedances are coupled, and more particularly relates to a method for fabricating a composite-material vibrating device that is capable of reflecting vibrations that have propagated from a vibrating member at the interfaces between the other material portions to thereby confine the vibrations in a portion within the interfaces.
2. Description of the Related Art
Conventionally, a structure in which casing substrates are laminated on the upper and lower surfaces of a piezoelectric vibrating element has been widely used for piezoelectric resonator components for use as piezoelectric resonators or piezoelectric filters. In this case, a space for permitting vibration of the piezoelectric vibrating portion of the piezoelectric element must be formed in the laminate. Thus, examples of methods that have been available include a method in which a depression for forming a cavity is provided in a piezoelectric-element-side surface of a casing substrate to be laminated and a method in which a region corresponding to a cavity is provided in an adhesive-applied area for forming the cavity before a casing substrate is laminated on a piezoelectric element.
As described above, in the laminated piezoelectric resonator components of the related art, a cavity for permitting vibrations of the piezoelectric vibrating portion must be formed. This makes it difficult to achieve miniaturization and cost reduction.
Meanwhile, Japanese Unexamined Patent Application Publication No. 10-270979 discloses a bulk acoustic wave filter having a laminated structure without a cavity. As shown in FIG. 13, in a bulk acoustic wave filter 211, a piezoelectric filter is configured by providing a large number of films on a substrate 212.
That is, in this laminated structure, a piezoelectric layer 213 is formed and electrodes 214 and 215 are provided on the upper and lower surfaces of the piezoelectric layer 213 to provide a piezoelectric resonator.
Layers made of silicon, polysilicon, or other suitable material are provided on the lower surface of the piezoelectric resonator to provide an acoustic mirror 219 having a laminated structure that includes a top layer 216, a middle layer 217, and a bottom layer 218. Also, an acoustic mirror 220 having a similar laminated structure is provided on the upper surface of the piezoelectric resonator and a passivation layer 221 is formed on the acoustic mirror 220 as a protection layer.
In the acoustic mirror 219, the acoustic impedance of the middle layer 217 is higher than the acoustic impedance of the top layer 216 and the bottom layer 218. In the acoustic mirror 220, similarly, the acoustic impedance of the middle layer higher than the acoustic impedance of the top and bottom layers.
In the bulk acoustic wave filter 211, the provision of the acoustic mirrors 219 and 220 on the piezoelectric resonator portion allows vibrations that have propagated from the piezoelectric resonator to be reflected back toward the piezoelectric resonator. Thus, this structure can be mechanically supported using the substrate 212 without affecting the resonance characteristics of the piezoelectric resonator portion.
The bulk acoustic wave filter 211 shown in FIG. 13 is configured such that the acoustic mirrors 219 and 220 reflect vibrations that have propagated from the piezoelectric resonator. In each of the acoustic mirrors 219 and 220, the top and bottom layers are provided on the corresponding upper and lower surfaces of the middle layer and the acoustic impedance of the middle layer is higher than the acoustic impedance of the top and bottom layers. Thus, a large number of material layers must be provided for the acoustic mirrors 219 and 220. Thus, while no cavity needs to be formed, a large number of material layers must be provided in the bulk acoustic wave filters 211, which makes it difficult to achieve a compact, particularly, low profile structure. The fabrication process is also complicated.
In addition, in the bulk acoustic wave filter 211, lateral vibrations in the piezoelectric resonator propagate and the vibrations that have alternately propagated are damped at side portions of the piezoelectric resonator. Thus, the side portions of the piezoelectric resonator portion are fixed, which poses a problem in that resonance characteristics of the piezoelectric resonator are deteriorated by the holding structures.
To overcome the shortcomings and problems of the related art described above, preferred embodiments of the present invention provide a composite-material vibrating device that is inexpensive, compact, and particularly suitable for a low profile application and that can be supported with little or no influence on vibration characteristics of a vibrating member using a relatively simple structure.
A composite-material vibrating device according to a preferred embodiment of the present invention includes a vibrating member that is made of material having a first acoustic impedance Z1 and that defines a vibration generating source, and at least three reflective layers that are coupled to corresponding outer surfaces located in at least three directions of the vibrating member and that are made of material having a second acoustic impedance Z2 that is smaller than the first acoustic impedance Z1. The composite-material vibrating device further includes holding members that are made of material that are coupled to surfaces opposite to the surfaces, coupled to the vibrating member, of the reflective layers and that are made of a material having a third acoustic impedance Z3 that is greater than the second acoustic impedance Z2. Vibrations that have propagated from the vibrating member to the reflective layers are reflected at interfaces between the reflective layers and the corresponding holding members.
In preferred embodiments of the present invention, vibrations that have propagated from the vibrating member to the reflective layers are reflected at the interfaces between the reflective layers and the corresponding holding members. With this arrangement, vibrations of the vibrating member are securely confined in regions within the interfaces. Thus, the composite-material vibrating device of preferred embodiments of the present invention can be supported by the holding members without preventing the vibration of the vibrating member using a relatively simple structure. Thus, there is no need to form a cavity for permitting vibration of the vibrating member, which allows for significant reduction in the size and cost of the composite-material vibrating device. In addition, since the acoustic impedance Z2 is preferably smaller than the acoustic impedances Z1 and Z3 to thereby reflect vibrations at the interfaces, the vibration mode of the vibrating member used is not particularly limited. Thus, it is possible to easily provide composite-material vibrating devices utilizing various vibration modes. Preferably, the vibrating member has a substantially rectangular parallelepiped or substantially cubic shape and the reflective layers are provided on at least three outer surfaces of the vibrating member. Thus, the composite-material vibrating device can be supported using an outer surface, which is located in any one of the at least three directions, of the composite-material vibrating device.
Preferably, the ratio Z2/Z1 of the second acoustic impedance Z2 to the first acoustic impedance Z1 is about 0.2 or less. This can further ensure that vibrations that have propagated from the vibrating member to the reflective layers are reflected.
Preferably, the ratio Z2/Z3 of the second acoustic impedance Z2 to the third acoustic impedance Z3 is about 0.2 or less. This can further ensure that vibrations that have propagated from the vibrating member to the reflective layers are reflected at the interfaces between the reflective layers and the corresponding holding members.
Preferably, propagating vibrations that propagate in the reflective layers from the vibrating member toward the holding members are reflected at the interfaces between the reflective layers and the corresponding holding members, and the amplitude direction of the propagating vibrations is substantially perpendicular to the propagating direction of the propagating vibrations. This arrangement allows the thickness of the reflective layers to be reduced compared to a case in which the amplitude direction of the propagating vibrations is parallel to the propagating direction.
In preferred embodiments of the present invention, while the vibrating member is not particularly limited, the vibrating member preferably is made of an electromechanical coupling conversion element. Further, the electromechanical coupling conversion element is preferably a piezoelectric element or an electrostriction element.
The reflective layers may each include a plurality of material layers having different acoustic impedances. In this case, selecting the acoustic impedances of the plurality of material layers can facilitate the adjustment of the acoustic impedance of the reflective layers.
The distance from the interfaces between the reflective layers and the vibrating member to the interfaces between the reflective layers and the corresponding holding members is preferably in the range of nxc2x7xcex/4xc2x1xcex/8 (n is an odd number), where xcex is the wavelength of propagating vibrations that propagate in the reflective layers toward the holding members in response to vibrations from the vibrating member. This allows the propagating vibrations to be more effectively reflected at the aforementioned interfaces and allows a further reduction in influence on the vibrating member which results from the support arrangement.
Preferably, the holding members have a plurality of capacitance electrodes for constituting a capacitor. Thus, the holding members are utilized to constitute the capacitor. Consequently, the combination of the vibrating member and the capacitor allows the provision of a miniaturized vibrator or other suitable component.
Another preferred embodiment of the present invention provides a method for fabricating a composite-material vibrating device in which a plurality of material portions having different acoustic impedances are coupled. In this case, a composite-material vibrating device according to preferred embodiments of the present invention has a structure in which holding substrates are coupled to a plate vibrating member with reflective layers interposed therebetween. The acoustic impedance Z2 of the reflective layers is preferably smaller than the acoustic impedances Z1 of the vibrating member and the acoustic impedance Z3 of the holding substrates. As a result, vibrations that have propagated from the vibrating member are reflected at the interfaces between the reflective layers and the corresponding holding substrates. This makes it possible to achieve mechanical support using the holding substrates without affecting the vibration characteristics of the vibrating member.
Another preferred embodiment of the present invention provides a method for fabricating a composite-material vibrating device in which a plurality of material portions having different acoustic impedances are coupled. The fabrication method includes a step of preparing a plate vibrating member having a first acoustic impedance Z1 and a holding substrate having a third acoustic impedance Z3 and a step of applying a fluid material to one surface of the vibrating member or holding substrate such that the thickness thereof becomes a thickness for forming a reflective layer having a desired thickness. After being cured, the fluid material becomes the reflective layer having a second acoustic impedance that is smaller than the first and third acoustic impedances. The fabrication method further includes a step of curing the fluid material and, a step of laminating the vibrating member and the holding member with the fluid material interposed therebetween, before or after the fluid material is cured. It is therefore possible to ensure the formation of the reflective layer having a desired thickness.
The step of applying the fluid material may be performed in such a manner that a strip protrusion is formed on the surface, to which the fluid material is to be applied, of the vibrating member or the holding substrate so as to correspond to the thickness of the fluid material to be applied and the fluid material is applied to a region that is surrounded by the strip protrusion. Application of the fluid material to a region that is surrounded by the strip protrusion allows, in accordance with the thickness of the strip protrusion, high-accuracy control of the thickness of the fluid material to be applied. As a result, it is possible to form a reflective layer that is improved in thickness accuracy.
Preferably, the strip protrusion is integrally formed with the vibrating member or the holding substrate using the same material. In this case, there is no need to prepare the strip protrusion as a separate member. Only preparing the vibrating member or the holding member with which the strip protrusion is integrated can facilitate the formation of a reflective layer that is improved in thickness accuracy.
The step of applying the fluid material may be performed in such a manner that a depression having a depth that corresponds to the thickness of the fluid material to be applied is formed in one surface of the holding substrate and the fluid material is applied in the depression. Since the fluid material is applied in the depression, the thickness of the fluid material to be applied can be accurately controlled in accordance with the depth of the depression. As a result, it is possible to form a reflective layer that has improved thickness accuracy.
In the step of applying the fluid material, the fluid material may contain a spherical or columnar substance having a thickness that is substantially the same as the thickness of the reflective layer, and the holding substrate and the vibrating member are laminated with the fluid material before being cured and then the fluid material is cured. In this case, since the vibrating member and the holding member are laminated with the fluid material containing the spherical or columnar substance, the reflective layer having a thickness corresponding to the size of the spherical or columnar substance is reliably formed. As a result, it is possible to provide a reflective layer that is improved in thickness accuracy.
The step of curing the fluid material may be performed before the vibrating member and the holding member, to one of which the fluid material being applied, are laminated together.
The step of curing the fluid material may be performed after the vibrating member and the holding member, to one of which the fluid material being applied, are laminated together. In this manner, the fluid material may be cured either after or before the lamination.
Another preferred embodiment of the present invention provides a method for fabricating a composite-material vibrating device in which a plurality of material portions having different acoustic impedances are coupled. The fabrication method includes a step of preparing a plate vibrating member having a first acoustic impedance Z1 and a holding substrate that is made of material having a third acoustic impedance Z3 and a step of preparing a reflective-layer-constituent plate member having a second acoustic impedance Z2 that is smaller than the first and third acoustic impedances Z1 and Z3. The fabrication method further includes a step of processing the reflective-layer-constituent plate member so as to provide a reflective layer having a desired thickness and a step of laminating the vibrating member and the holding substrate with the reflective layer having the desired thickness. It is therefore possible to secure the provision of a composite-material vibrating device having reflective layers with a desired thickness.
Accordingly, preferred embodiments of the present invention ensure the provision of a composite-material vibrating device having reflective layers that are superior in thickness accuracy.
In preferred embodiments of the present invention, while the vibrating member is not particularly limited as long as it functions as a vibration generating source, it is preferably configured with an electromechanical coupling conversion element. Examples of the electromechanical coupling conversion element include a piezoelectric element and electrostriction element.
Other features, elements, characteristics, steps, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.